The present invention relates to hard rock drilling, and more particularly, to a continuous chain bit having a self-contained mechanism for downhole cycling utilizing common bit movements and drilling mud pressure.
Continuous chain drill bits are known in the prior art. Basically, a chain is mounted in a housing forming the bit. The outer face of chain links are provided with diamonds and/or synthetic diamond compacts and multiple links are selectively positioned at the bottom of the drill bit to engage the hard rock and drill a borehole. The drilling action of the bit is generated by the rotation of the entire body of the bit thereby moving the diamond-studded links in a rotative pattern against the rock. When the drilling efficiency of the bit decreases to the point where movement is too slow for economic operation, thus indicating that the diamonds are worn, the bit is lifted from the bottom of the borehole and the chain is cycled to bring the next multiple of chain links into the working position. Continuous chain bits are thus, in theory, very efficient, since no longer is the drill bit required to be removed from the borehole when the diamonds are worn. A bit can remain in the borehole through five or more drilling cycles, saving substantial time and expense normally required to raise a bit and replace it.
Heretofore, the continuous chain drill bits that have been tried have been generally unsuccessful. The bits have been found lacking in ease of cycling the chain, the reliability of the working chain links at the bottom of the borehole, and in general, the ruggedness and reliability needed in a drill bit, especially one designed to drill in hard rock, such as granite or the like. Prior designs have suffered from lack of positive means to position and lock the parts in position, especially centering and locking the chain in position during drilling. Purely hydraulic mechanisms, previously used for cycling of the chain, have proven unreliable and inefficient, and generally the bits have required movements during chain cycling that are not compatible with the normal drilling practice. In addition, efficient transfer and distribution of the drilling mud to the working links and the provision for links of greater width to provide a wider drilling path have not heretofore been obtainable.
Thus, in accordance with the present invention, it is an object to provide a new, improved continuous chain drill bit overcoming the above shortcomings of the prior art.
It is a more specific object of the present invention to provide a continuous chain drill bit cyclable while downhole by simple operations, fully compatible with normal drilling practice and utilizing a unique combination of mechanical movements and hydraulic actuation.
It is still another object of the present invention to provide a continuous chain drill bit wherein actual movement between the drilling head assembly and the support body for the bit is utilized to cycle the chain by bodily movement of the chain while holding the chain in position relative to the support body.
It is still another object of the present invention to provide a drill bit having a head assembly that is compact, rugged and reliable in operation.
Still another object of the present invention is to provide a drill bit having a cyclable chain that is moved by simple mechanical movement and centered at the end of the movement by hydraulic means.